

593 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



ments represented, by the Lewis and Bearpaw shales over the coal-bearing for- 

 mations. 



"As far up in the series as brackish-water fossils are found they occur in 

 usually thin beds intercalated amongst the fresh-water strata, showing that 

 the two elements of the fauna had separate habitats. . . . These mollusks 

 evidently lived in tidal waters connected somewhere with the open ocean" (281, 

 282). 



The most interesting biological side of the question connected with 

 these beds is of course furnished by the wonderful dinosaur assemblage, 

 among which the Ceratopsia are the more conspicuous because more com- 

 monly found. These forms have been well described by Hatcher . and 

 Lull. The dinosaurs represented are : Triceratops Jiorridus, T. flabellatus,. 

 T. prorsus, T. serraius, T. sulcatum, T. obtusus, T. elatus, T. brevicornis, 

 T. calicornis, Dicer at ops hatcheri, Torosaurus latus, and T. gladius, as 

 well as Tracliodon, Tyrannosaurus rex, and OrnWiomimus. The mammal 

 remains are very fragmentary, and all pertain to archaic forms — that is, 

 Mesozoic types — which also range into the basal Eocene beds. The dino- 

 saurs, however, are as yet not known to range above the Cretacic. 



The fresh-water mollusks are varied, the fauna consisting of about 25 

 named species of Unio, together with Anodonta, Splicerium, CorbicuJa 

 subelliptica, Viviparus, Tulotoma thompsoni, Campeloma (several spe- 

 cies), TJiaumastus, Goniobasis tenuicarinata, Physa, Helix, Limnea, and 

 Bulimus. This fauna is quite distinct from all those of the same habitat 

 which succeed it in the American Eocene. 



The brackish-water faunas have Ostrea sub trigonal is, 0. glabra, Corbula 

 subtrigonalis, C. undifera, Corbicula cytheriformis, C. subelliptica, C. 

 occidentalis, C. fracta, Anomia micronema, Neritina baptista, N. volvili- 

 neata, Melania Wyoming ensis. These are likewise Cretacic forms. 



Of land plants, in Converse county alone are 48 named species, of which' 

 5 are figs and 2 are palms. The flora indicates a subtropical climate. In 

 this connection it should be stated that the floras of the late Cretacic and 

 Eocene show no marked differences, the change being one of species, not 

 of different families and genera (information supplied by Knowlton). 



The vertebrate evidence shows close relationship with that of the Judith 

 Eiver fauna, which is known to be Cretacic, and lies beneath a thousand 

 feet or more of marine Cretacic beds. The whole fauna of the Ceratopsia 

 beds is decidedly Cretacic, and there is nothing to suggest the Cenozoic 

 unless it be the archaic mammals, of which two or three genera are also 

 known in the Torrejon (Eocene), where the mammals, and those of the 

 Puerco (Eocene) as well, are all of Mesozoic origin. 



